1. Field of the Invention
The present invention relates to pacemakers. More particularly, the invention concerns cardiac electrodes for use with pacemakers, and especially pacemakers designed to be compatible with MRI diagnostic apparatus.
2. Description of Prior Art
The metallic cardiac electrodes and leads used in conventional cardiac stimulation and monitoring devices have always been a problem. They tend to fatigue, corrode, and break. Their physical properties (corrosion, strength, chemical activity, etc.) limit the materials which can be used to titanium, platinum metals, their alloys, to certain stainless steels, and to special structures to limit fatigue (such as spring coils, metal cladding, multiple strands, etc.) With respect to metallic leads, a leaky interface is often produced between the metal and the insulating sheath that surrounds the leads.
The problem of metallic leads has been addressed by applicant's assignee in an effort to provide a pacemaker that is compatible with MRI diagnostic imaging procedures. See copending Ser. Nos. 09/864,944 and 09,865,049, both filed on May 24, 2001, and copending Ser. Nos. 09/885,867 and 09/885,868, both filed on Jun. 20, 2001. In these copending patent applications, the contents of which are fully incorporated herein by this reference, MRI compatible/safe pacemakers are disclosed for both implantable and wearable use. The disclosed pacemakers feature photonic catheters carrying optical signals in lieu of metallic leads carrying electrical signals in order to avoid the dangers associated with MRI-generated electromagnetic fields.
The devices of the copending applications also use only non-ferromagnetic materials and attempt to minimize the number of metal components of any kind. In accordance with these goals, the copending applications propose electrodes that are made from non-ferromagnetic metals such as titanium, platinum, and platinum-containing alloys. In addition, the copending applications advise that non-metals may also be used to provide the electrodes. It is the purpose and goal of the present invention to address such non-metallic electrodes and to propose specific nonmetallic electrode constructions that could be used to advantage in an MRI compatible/safe pacemaker, as well as in pacemakers and other electrical stimulation devices that are not necessarily designed for MRI compatibility and safety.